How do i add weights to bones that i added after i parented the armature to the mesh?
Find out the names of the newly-added bones

It's listed in your Properties Panel, under Item.



Create Vertex Groups on your Mesh with those names

Bones look for vertex groups with corresponding names to deform.



Paint on some weight



You can do this from Weight Paint Mode, or alternatively use the Weight slider to specify a weight before clicking Assign. Always pay attention to which vertex group you have selected when weight painting.